This tutorial section on LTE basics covers following sub topics:
Main page features terminologies Frame TDD FDD Channel types PHY stack throughput VoLTE CA cell search network entry Timers PSS vs SSS Security LTE Bands EARFCN Hotspot router
This page on LTE terminology covers LTE and LTE advanced technology related terms. It include terms eNB,eNodeB,UE,OFDMA,SC-FDMA,LTE frame,Resource block(RB), Resource Element(RE),Slot,sub frame,reference signal, synchronization signal,S-GW,MME,X2 interface, S1 interface, Uu interface, Control channel, data channel,LTE channel types,logical channel, transport channel, physical channel, P-SS,S-SS,PBCH,PDSCH,PDCCH,PCFICH,PCH,RS,SRS,DMRS,PRACH, PUSCH,PUCCH, carrier aggregation,voice over LTE etc.
eNB or eNodeB It is similar to Base station which is used in GSM networks. Also called as eNodeB.
UE: It is similar to mobile subscriber.
OFDMA: Orthogonal Frequency Division Multiple Access, used in physical layer of LTE Downlink.
SC-FDMA: Single Carrier Frequency Division Multiple Access, used in physical layer of LTE Uplink.
LTE Frame: LTE frame are of 2 types TDD and FDD. In both the cases, frame is composed of 10 sub frames and each sub frame is made of 2 slots. Frame size is 10ms.
Resource Block (RB): It is the smallest block of resource that can be allocated to UE by eNB;
it is 12 subcarriers for 7 symbols.
Resource Element (RE): The smallest unit of radio resources, one subcarrier for one symbol.
Slot: 7 consecutive symbols for short Cyclic Prefix, 6 symbols for long cyclic prefix.
Sub frame: 2 consecutive timeslots.
Reference Signal: Similar to pilot carrier and is used for channel estimation at the receiver.
Synchronization signal: There are two synchronization signals, Primary and secondary. Both are transmitted in slot 0 and slot 10 in all the frames. It is same as preamble used in earlier systems and used for time, frequency synchronization purpose.
S-GW: Serving Gateway
MME: Mobility Management Entity
X2 interface: Interface used between eNodeB and eNodeB.
S1 interface: Interface used between eNodeB and core network interface (MME/S-GW).
Uu interface: This is the air interface used between eNodeB and UE.
Control channel: This channel carry control information used to make, maintain and terminate the connection. Used for the transfer of control plane information in LTE.
Data channel: This channel carry traffic information. Used for the transfer of user plane information.
Channel structure in LTE:
LTE adopts a hierarchical channel structure. LTE defined three channel types i.e. logical,transport and physical channels. Each associates with a service access point (SAP). (SAP) between different layers. These channels are used by lower layers to provide services to the upper layers.
Logical Channels: What to Transmit.
They are used by MAC layer to provide services to RLC layer. Each logical channel is defined as per type of information it carries. In LTE, there are two categories of logical channels depending on the service they provide: control channels and traffic channels. The new LTE categories M1 and NB1 are added in LTE 3GPP Release 13.
Transport Channels: How to Transmit.
PHY uses transport channel to offer services to the MAC layer. It is characterized by how and with what characteristics data is transferred over the air.
Physical Channels: Actual Transmission
Each physical channel maps to a set of resource elements in the time frequency grid that carry information from upper layers. The basic entities that make a physical channel are REs and RBs. A resource element is one subcarrier by one OFDM symbol and typically this could carry one (or two with spatial multiplexing) modulated symbol(s). A resource block is a collection of resource elements and in the frequency domain this represents the smallest quanta of resources that can be allocated.
P-SS: Primary synchronization signal
S-SS: secondary synchronization signal
PBCH: Physical Broadcast Channel
PDSCH: Physical Downlink Shared Channel
PDCCH: Physical Downlink Control Channel
PCFICH: Physical Control Format Indicator Channel
PHICH: Physical Hybrid ARQ Indication Channel
PCH: Paging channel
RS: Reference Signal, used both in uplink and downlink
SRS: Sounding reference signal, used in uplink
DMRS: Demodulation Reference Signal
PRACH: Physical Random Access Channel used in uplink
PUSCH: Physical Uplink Shared Channel
PUCCH: Physical Uplink Control Channel